A powerful decision

This is a classic Of Wings & Things from the 1980s. GAN will continue to run the late Mr. Bowers’ column for the enjoyment of his readers.

One of the major decisions for any airplane designer is powerplant. Sometimes the choice is made for the designer when the customer who ordered the plane specifies the engine to be used.

In the case of a company that’s developing a new aircraft on its own, the choice can be particularly tough: a well-proven engine that may soon be obsolete, or a new and unproven model that seems to deliver more power for its weight and has good potential for future growth?

The Boeing Airplane Co., and others, were in the latter situation early in 1928. Boeing was designing a new two-seater for the primary training market, and the choice of engines wasn’t very wide. The faithful old watercooled Curtiss OX-5, with 90 hp, was clearly on the way out, and the popular Wright J-5 “Whirlwind” was too big for that class of airplane. There wasn’t much choice in between at the time except the brand-new and highly innovative Fairchild-Caminez, a compact air-cooled radial.

Under development since 1925, the Caminez was now on the market and promised to revolutionize the engine business. Instead of conventional connecting rods and crankshaft, the Caminez used a double-lobe cam and rollers, and obtained four piston-strokes per revolution instead of two. This arrangement gave two power strokes per cylinder per cycle instead of one at a propeller speed half that of a regular engine. This made for a very efficient slow-turning propeller. The cams also permitted an even number of cylinders in a single-row engine where conventional radials always had an odd number. This, plus the different innards, supposedly made for much smoother running.

The early engines were advertised as producing 150 hp at 1,200 rpm, later reduced to 145 at 1,100. By the time the engine was awarded Engine Approved Type Certificate (ATC) No. 1 in June 1928, it was rated 120 hp at 960 rpm.

Boeing built two Model 81 trainers to use the Caminez, and the first one flew in March 1928. The second went to the U.S. Navy in June for a fly-off trainer competition and received the Navy designation of XN2B-1.

In spite of the rosy promise in the Fairchild literature and the demonstrated efficiency of the new engine under testing, it simply didn’t stand up in an operational environment. Other manufacturers dropped the Caminez as an option for their standard models and the Navy sent the XN2B-l to Wright Aeronautical in January 1929 for installation of the brand-new 165 hp, Wright “Whirlwind.” This went on to become a very popular and dependable trainer engine.

Boeing soon replaced the Caminez in the Model 81 it still had and installed another new-model engine, the Axelson A, in December 1928. This was a seven cylinder radial delivering 150 hp at 1,800 rpm, but was so new that it didn’t have an ATC. With the new engine installed, Boeing redesignated the plane as Model 81-A and turned it over to its subsidiary, the Boeing School of Aeronautics.

The new Axelson didn’t stand up either, and the 81-A couldn’t qualify for the necessary ATC for commercial operation. The school then did some engineering on its own and replaced the 150 hp Axelson with a later ATC’d model that delivered only 115 hp. The airplane, now designed the 81-B, was then approved for commercial use.

The 115 hp Axelson, too, was a headache. Examples used in the school’s other trainers, Boeing 203s, were soon replaced by 165 hp Wright J-6-5s and a J-6-5 was put into the 81-B in October 1932, thereby making it the 81-C.